JPH0365029B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser, and particularly to a semiconductor laser of the type that emits laser light from the top surface of the device.

Semiconductor lasers have many characteristics such as being compact, operating with high efficiency, and being capable of high-speed direct modulation using a drive current, and are extremely suitable as light sources for optical communications, optical information processing, and the like. Until now, semiconductor lasers have mainly been of the type that extracts optical output from the sides of the element, such as Fabry bellow type elements or similar devices, which extract optical output from the cleavage plane as a mirror of the laser. In order to make the coupling with optical fibers etc. easier and more efficient, these types of elements need to be placed close to the edges of the heat sink, which not only complicates the fusing process, but also makes it difficult to bond them with cleaved surfaces on the sides. In this case, the direction of the cavity within the semiconductor laser pellet is inevitably limited, and when integrating with other devices, the positional relationship is limited, so freedom in device design is lost. It was the cause of this.

For this reason, recently, semiconductors have been developed that do not emit output light from the side surfaces or take out output light from the cleavage plane.An example of this is Applied Physics Letters (Appl. Phys. Lett.) Volume 27, No. 295- Item 297 (1975) contains a paper using this type of semiconductor laser. This type of semiconductor laser consists of an n-type substrate, an n-type guide layer, and a p-type semiconductor laser.
It consists of a p-type active layer, a p-type guide layer, and an n-type active layer.
A diffraction grating is formed between the mold substrate and the n-type guide layer, and both side surfaces serve as cleavage planes. The wave period, or pitch Λ, of a diffraction grating can be expressed in its most basic form as λ/n, where λ is the wavelength of the laser light in free space and n is the equivalent refractive index, and this represents the second-order Bragg reflection. This indicates that the semiconductor laser is used. With such a configuration, output light is extracted in a direction perpendicular to the pn junction surface.

However, in the above semiconductor laser device, the diffraction grating that uses high-order (second-order) Bragg reflection also serves as a mirror for laser oscillation, which reduces oscillation efficiency and causes an increase in the oscillation threshold. However, both sides must be cleavage planes. Furthermore, since light is emitted over the entire length of the device, the coupling efficiency is reduced when optical fibers are coupled to each other.

In the above, some semiconductor lasers have a diffraction grating that uses first-order Bragg reflection instead of a diffraction grating that uses high-order Bragg reflection, but these semiconductor lasers have output light parallel to the p-n junction surface. This type of radiation is emitted in the direction, but not in the vertical direction, that is, from the top surface.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor laser which can emit output light from the top surface of the device without forming cleavage planes on both sides of the device.

Another object of the present invention is to obtain a low threshold semiconductor laser having a small emission surface while emitting output light from the upper surface of the device.

In order to achieve the above object, the present invention has a diffraction grating divided into a mirror part that uses first-order Bragg reflection and an output extraction part that uses higher-order Bragg reflection. It is.

According to the present invention, a semiconductor substrate, an active layer grown on the substrate and having a desired refractive index and a forbidden band width, and a refractive index provided on at least one of both surfaces of the active layer have the desired refractive index. a plurality of semiconductor layers including a guide layer whose refractive index is smaller than the desired bandgap width and which is larger than the desired bandgap width; and an electrode layer provided on a side of the plurality of semiconductor layers opposite to the semiconductor substrate. and wherein at least one surface of at least one of the plurality of semiconductor layers is configured to form a diffraction grating with an opposing layer, wherein the electrode A portion of the inner side of the layer is configured to be substantially transparent to the output light of the semiconductor laser, and the pitch of the diffraction grating is high in a region corresponding to the transparent portion of the electrode layer. A semiconductor laser characterized in that the length is set so that the following Bragg reflection is used, and the length is set so that the first-order Bragg reflection is used in a region corresponding to the part that is not a part of the transparent part. can get.

Next, it will be explained in detail using the drawings.

FIG. 1 shows a perspective view of an embodiment of the present invention. In Figure 1, 1 is an n-type substrate, and 2 is 1 with pitch Λ=λ/2n on the (001) plane.
A first diffraction grating using the following Bragg reflection, 3 a diffraction grating using a second-order Bragg reflection expressed by pitch Λ=λ/n, 4 a diffraction grating whose forbidden band width is approximately in wavelength.
One guide layer of 1.1 μm n-type InGaAsP, 5, has a forbidden band width corresponding to approximately 1.3 μm in wavelength.
The active layer of InGaAsP, 6, has a forbidden band width of approximately
The other guide layer is made of 1.1 μm P-type InGaAsP, 7 is a cladding layer made of p-type InP, 8 is a Zn diffusion region forming a current injection stripe, and 9 is made of n-type InP. 10 is a p-side electrode, 11 is an n-side electrode, and 12 is a window provided inside the n-side electrode 11 for extracting light output. Here, the direction of the stripes of the Zn diffusion region 8 forming the current injection stripes is substantially perpendicular to the gratings of the first and second diffraction gratings 2 and 3. Also, the thickness of the active layer 5 is approximately
The thickness of guide layers 4 and 6 are both approximately 0.15 μm.
It is 0.2 μm. Furthermore, the periods Λ ₁ and Λ ₂ of the irregularities of the diffraction gratings 2 and 3 are approximately 0.2 μm and approximately 0.4 μm, respectively.

In the above structure, when a current is injected into the active layer 5 in the vicinity of the Zn diffusion region 8, laser oscillation occurs in the direction of the stripe. On this occasion,
The light seeping into the first diffraction grating 2 interacts with it to select the oscillation wavelength. Also the second
A part of the laser oscillated light by the diffraction grating 3 is emitted in a direction perpendicular to the p-n junction surface, and is outputted from an optical output window 12 provided in a part of the n-side electrode 11. is obtained.

Note that in the configuration shown in FIG. 1, the main parts include an n-type substrate 1, an n-type guide layer 4, an active layer 5, and a p-type guide layer 6, which is different from the conventional structure described earlier. It is exactly the same as a semiconductor laser, but the difference is that the diffraction grating is composed of two different parts of the pitch, that there is an internal output extraction window at the top of the element, and that both sides are This means that it does not have to be a cleavage plane.

Here, the manufacturing method of this example will be briefly described. First, an n-type InP substrate 1 having a (001) plane on its surface is prepared, and diffraction gratings 2 and 3 are carved on its surface. Photolithography technology is applied to form the diffraction grating. Next, an n-type InGaAsP guide layer 4 (with a forbidden band width of
1.1 μm), non-doped InGaAsP active layer 5 (gap band width 1.3 μm), p-type InGaAsP guide layer 6 (gap band width 1.1 μm), p-type InP cladding layer 7, and n-type InP cap layer. Grow 9 sequentially. Next, Zn diffusion region 8 is formed using SiO ₂ as a mask.
Finally, a p-side electrode and an n-side electrode 11 having a window 12 from which light output is taken out are formed.

The present invention has been described above with reference to the drawings. In this embodiment, an anti-melt layer is provided between the active layer 5 and the guide layer 6 to suppress the meltback of the active layer 5 that occurs when the guide layer 6 is grown. A back layer may also be provided. Alternatively, the guide layer 6 may also serve as an anti-melt back layer. Also the first and second
When the diffraction gratings 2 and 3 are formed on the InP substrate 1, the guide layer 6 may be omitted.

Furthermore, in this example, the diffraction grating is placed on the InP substrate 1.
Although the diffraction grating is formed on the guide layer 6, the diffraction grating may be formed on the guide layer 6, or may be provided in parallel on both. Furthermore, in this embodiment, a quaternary InGaAsP system was used as the composition of the semiconductor laser, but the composition is not limited to this, and it goes without saying that other compositions such as a GaAs system or a PbSnTe system can also be used.

Finally, the advantages of the present invention are that it does not require a cleavage plane, making it easy to cut out pellets, and since the region where light output can be obtained is limited, the coupling efficiency to the optical fiber is high, and the diffraction grating is Since the laser oscillation is obtained by the feedback used, a single-axis mode semiconductor laser can be realized, and the emission direction of the optical output is perpendicular to the p-n junction, so
Unlike a laser that obtains optical output from a cleavage plane, the installation position on the mount is not restricted when mounted.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention. Explanation of symbols: 1 is InP substrate, 2 and 3 are diffraction gratings, 4 is guide layer, 5 is active layer, 6 is guide layer,
7 is a cladding layer, 8 is a Zn diffusion region, 9 is a cap layer, 10 is a p-side electrode, 11 is an n-side electrode, and 12 is a window for extracting light output.

Claims (1)

[Claims] 1. A semiconductor substrate, an active layer grown on this substrate having a desired refractive index and a forbidden band width, and a refractive index provided on at least one surface of both surfaces of the active layer that is lower than the desired refractive index. a plurality of semiconductor layers including a guide layer that is small and whose forbidden band width is larger than the desired forbidden band width; and an electrode layer provided on a side of the plurality of semiconductor layers opposite to the semiconductor substrate; In the semiconductor laser, in which at least one surface of at least one semiconductor layer among the plurality of semiconductor layers is configured to form a diffraction grating with an opposing layer, A portion of the diffraction grating is configured to be substantially transparent to the output light of the semiconductor laser, and the pitch of the diffraction grating is such that a high-order Bragg reflection occurs in a region corresponding to the transparent portion of the electrode layer. A high-order Bragg reflection region is set to a length that uses first-order Bragg reflection, and a first-order Bragg reflection region whose pitch is set to a length that uses first-order Bragg reflection in the region corresponding to the remaining part excluding the transparent part. 1. A semiconductor laser comprising: a Bragg reflection region; the higher-order Bragg reflection region is sandwiched between the first-order Bragg reflection regions.